WEDNESDAY, April 27, 2011 (Health.com) — Several years ago, an 81-year-old woman with a raised patch of dry skin on her arm visited Mississippi dermatologist John Abide, MD. Although the lesion looked only slightly abnormal, a series of lab tests revealed that it was a symptom of leprosy.
“I thought, ‘Leprosy, are you kidding me?’” says Dr. Abide, whose practice is in Greenville.
His surprise was understandable. Each year only about 150 people in the U.S. are infected with leprosy, a bacterial disease that can lead to nerve damage and disfigurement. In most cases, people are infected after being exposed to saliva from an infected person, usually while traveling to parts of the world, such as Africa and Asia, where the disease is more prevalent. But Dr. Abide’s patient didn’t fit this description.
A new study in the New England Journal of Medicine may provide an explanation for her case: armadillos. The leathery shelled mammals, which can be found in 10 states throughout the southeastern U.S., are the only animals besides humans known to carry leprosy.
There have been several anecdotal reports of leprosy in humans who have handled, killed, or eaten armadillos, or who may have been indirectly exposed by gardening in soil where the animals burrow, as was the case for Abide’s patient. But until now, experts haven’t been able to confirm that armadillos could pass the disease to humans.
The study provides the strongest evidence to date. Researchers analyzed the genomes of leprosy-causing bacteria collected from seven patients and one armadillo. After identifying specific strains of the bacteria, they compared them with a larger group of infected people and armadillos from around the world.
Of the 50 patients and 33 wild armadillos the researchers analyzed from the U.S., 25 patients and 28 armadillos shared a genetically identical strain of leprosy bacteria. And at least 8 of the 25 patients carrying the strain reported contact with armadillos.
“It’s difficult to demonstrate specific causality,” says Richard Truman, PhD, one of the study authors and the chief of microbiological research at the National Hansen’s Disease Program, in Baton Rouge, La. (Leprosy is also known as Hansen’s disease.) However, he adds, the chance that the humans with the armadillo-specific strain were infected by some other means is about 1 in 10,000.
The armadillo population in the U.S. has been estimated at 30 to 50 million, and studies suggest that, in some places, up to 15% have leprosy. For now the infected animals are concentrated in Texas, Louisiana, Mississippi, Arkansas, and Alabama, but the armadillo population appears to be spreading north and east and could bring leprosy with it.
Truman says that people in those areas may eventually see a minor increase in risk, but so far leprosy has not been detected in animals on the East Coast. “Leprosy is a rare disease and will remain a rare disease,” he says.
Next page: Doctors may miss signs of leprosy